Touchscreens have been increasingly incorporated into mobile devices such as smart phones, tablets, and laptops in recent years. Touchscreen devices that serve as phones typically implement a standard 12-key phone keypad using soft keys demarcated on the touchscreen for each of the 12 keys. The standard 12-key phone keypad is used both for entering numbers and for selecting letters for text entry. For example, on an English 12-key keypad, the center button on the top row is for the number “2” and the letters “a,” “b,” and “c.”
Challenges have arisen in implementing a standard 12-key phone keypad on a touchscreen for text entry in character-based languages such as Japanese and Chinese. Character-based scripts in which each character represents a word are especially difficult to usefully implement because of the large number of characters. Character-based scripts in which each character represents a syllable (syllabic character) of a word are typically favored for text entry. In Japanese, the use of syllabic kana characters is therefore more common than use of kanji characters for text entry from a 12-key phone keypad.
Kana characters, however, present their own difficulties. There are still a larger number of kana characters than Roman letters (e.g., a, b, c), and some syllables are formed by combining a kana character with a modifier. Previous attempts at implementing a 12-key kana character keypad on a touchscreen assigned five kana characters to one soft key, with a first character displayed on the soft key and the other four characters selectable by sliding up, down, left, and right, respectively, for each of the other four characters. Such an arrangement of characters is not intuitive to mobile device users, causing users to experience a frustrating period of time during which the user slowly learns the location of each character. Additionally, in previous attempts, the user had to manually select a kana character modifier.